1. Field of the Invention
The present invention relates to a method of manufacturing aluminum gallium nitride/gallium nitride (AlGaN/GaN) high electron mobility devices for use in high-power, high-frequency device applications, to controlling or compensating charge within the channel of such high electron mobility devices, and the use of buffer layers to adaptively improve substrate resistivity.
2. Background
The aluminum gallium nitride/gallium nitride hetero-interface or heterojunction creates a planar region of high charge and high mobility electrons called a two-dimensional electron gas (2DEG), and is commonly used in high electron mobility devices. However, typical performance problems with gallium nitride based high electron mobility devices include dispersion related to unintentional traps in the nominally undoped or intrinsic gallium nitride buffer layer. These traps result in reduced channel charge in the two dimensional electron gas, current slump during device operation and reduced device lifetimes, among other problems. Also, AlGaN/GaN high electron mobility devices are planar growth structures that are typically depletion-mode devices that are normally-ON in their unbiased state, so that electrical current flows between source and drain contacts even when voltage is not applied to a corresponding gate contact. For electrical power switching applications, normally-OFF or enhancement-mode devices are preferable, such that charge does not flow between source and drain contacts in absence of applied voltage to the corresponding gate contact. Thus, there is a need to provide high electron mobility devices having improved performance, and also normally-OFF high electron mobility devices having improved performance.
Another performance problem that impacts high electron mobility devices is current leakage. To help reduce the impact of current leakage, there is a desire to manufacture high electron mobility devices on substrates having high resistivity in a range of 107-1012 ohms/cm. However, high resistivity substrates are expensive, and process yields are low. This contributes to the overall expense of high electron mobility devices. Thus, a cost-effective, high yield approach for providing high resistivity substrates is needed.